Along an assembly line, diapers and various types of other absorbent articles may be assembled by adding components to and otherwise modifying an advancing, continuous web of material. For example, in some processes, advancing webs of material are combined with other advancing webs of material. In other examples, individual components created from advancing webs of material are combined with advancing webs of material, which in turn, are then combined with other advancing webs of material. Once the desired component parts are assembled, the advancing web(s) and component parts are subjected to a final knife cut to separate the web(s) into discrete diapers or other absorbent articles. The discrete diapers or absorbent articles may also then be folded and packaged.
In some manufacturing operations, a continuous base web of material is advanced in a machine direction along a converting line. Discrete components and continuous webs are combined with the base web of material to form a continuous length of absorbent articles. As such, it may be necessary to accurately control the speed the base web to help ensure that the final knife cut is applied at desired locations to ensure the desired pitch length of the articles is maintained. As such, some registration control systems may utilize registration marks on the base web to determine if the base web is properly positioned with respect to the final knife. Registration marks may be configured in different ways. For example, in some instances, registration marks may be in the form of graphics printed on the base web. As the base web advances, the registration marks pass by a sensor that detects the presence the registration marks. The sensor provides a feedback signal that corresponds to when a registration mark is detected. A controller receives the feedback signal from the sensor and compares the feedback signal with a setpoint. Based on the comparison, the controller may change the speed of the base web.
At relatively low base web speeds, the registration control system may have adequate time to accurately change the web speed in response to feedback signals from the sensor. However, at relatively high base web speeds, time delays within registration control system may result in unstable and/or inaccurate control of base web speed. In turn, unstable and/or inaccurate base web speed control may result in misplaced final knife cuts on the continuous length of absorbent articles, resulting in damaged and/or defective absorbent articles. There may be various sources of time delays within the registration control system, such as time delays associated with the sensor and/or control loops. Some systems may attempt to compensate for the time delays by requiring the converting line to operate at relatively low base web speeds, which results in relatively lower production rates. Other systems may attempt to compensate for the time delays by utilizing high speed sensors, which may add to the complexity and cost of the manufacturing operation. Still other systems may attempt to compensate for the time delays by directly wiring the sensor input into a servo controller to control the base web speed.